Ever sit in a cinema and somewhere in between a bucket of popcorn and a lull in the action say to yourself, 'I've seen enough good and bad stuff to know what will and won't work - I could do that job in Hollywood'? Well, that thought accompanies every second mouthful during The Lone Ranger – along with the temptation to send off the CV when it's over.

While people in the film business love to say that for all the stars, sages and sure things, you never actually know how a movie is going to turn out, in this case somebody should have known something. What, with the 'brainwave' casting of Johnny Depp as Native American warrior Tonto; the past box office failure of summer westerns like Wild Wild West, Jonah Hex and Cowboys and Aliens, and younger viewers not having a history with the heroes, studio folk should've heard the alarm bells ringing long before the cameras started rolling. Older punters could, so why not them? No need for an answer straight away - you'll have loads of time to come up with one if you do buy a ticket.

Reuniting Depp with his Pirates of the Caribbean director Gore Verbinski (the writers, too), this isn't the complete mess that some have claimed - you've seen a lot worse. It is, however, a film that's unsure of exactly what it should be, the familiar, bloated feeling of Depp and Verbinski's later adventures on the high seas all the more perplexing given that they worked the Western genre so well together in the animated movie Rango.

Moving back and forth between a 1930s San Francisco fairground and 1860s Texas, The Lone Ranger is an origins story that spends over 45 minutes explaining what should've taken 15 (Raiders of the Lost Ark wasn't too bothered explaining how Indiana Jones became Indiana Jones eh?). The tone see-saws between slapstick and serious - and a bit of savagery, too - when Saturday morning serial was the way to go. There are two excellently realised railroad set-pieces at either end of the movie but too much unnecessary talking to get from one to the other, the script a bit of a runaway train in itself.

As expected, Depp gets all the best lines here and is the most interesting thing in the movie. But despite the subversion of the sidekick conventions, it feels wrong that a Native American actor isn't playing Tonto. And for all Hammer's hard work in the title role, you always wonder why Depp didn't play the Lone Ranger as a short-arsed serial bungler who becomes a hero despite himself, sending up the mythology of the Old West in the same way that he sent up swashbucklers so successfully in the first Pirates movie. There'll be a fifth instalment of it along soon enough; we won't get a second of this.

Amidst all the thinking about what went wrong (and arguments about stereotypes), The Lone Ranger puts one thing beyond doubt: you can be Dances with Wolves or Blazing Saddles, but you can't be both at the same time.